Square Body trucks(73-87, 73-91 on the SUVs and crew cabs) used a 15" wheel on the K models (half tons only). As far as I know, the 20/30 series trucks (3/4 & 1 ton) used a 16.5 wheel, then at some point they switched to a 16". Those are going to be 8 lugs though. The K10/K15 used a 15" that is 6 lugs. These were available in a plain steel wheel with the bumps for the dog dish hubcaps, and an optional aluminum wheel with a concave face and 8 holes in it (but still a 6 lug wheel). There's also a "truck rallye" wheel that's a "styled" steel wheel (what they called them in the brochures). These are 15"x 8" usually, may be 15x7 versions too.
Because of the popularity of everything Square Body, and the fact that all GM trucks before 1971 were 6 lugs(half tons anyway), and the lack of much aftermarket choice in 6 lug wheels years ago, though, these factory alloy wheels (what the aluminum wheels are called in the brochures) and Rallyes are harder to find, and often pricey when you do find them.
The standard white steel wheel for the dog dish caps should be easier to find.....
Hopefully this helps enlighten you!
